1. Field of the Invention
The present invention relates to a micro-pulsation fuel injection system with underpressure stabilizer, particularly to a micro-pulsation fuel injection system with underpressure stabilizer to be used in an internal combustion engine.
2. Description of Related Art
Conventional fuel supply systems of internal combustion engines include carburetors and fuel injection systems. A mechanical carburetor, using underpressure generated by flow in a tube, sucks in and vaporizes fuel. Vaporized fuel, having mixed with air, enters a cylinder of the internal combustion engine. However, being regulated by an inclination of an adjustment needle and flow control by the throttle valve, the quantity of fuel taken in is hard to control precisely. At full throttle, vaporization is imperfect, so that fuel wetting becomes worse.
A fuel injection system, on the other hand, has an electric fuel pump which pressurizes and pushes out fuel through a nozzle into an inlet manifold, where fuel is sprayed apart into fuel droplets. The fuel droplets subsequently mix with inlet air and enter a cylinder of the internal combustion engine. However, since fuel is ejected at high speed without being uniformly distributed, no uniform mixture of fuel and air is attained, so that fuel is wetted at walls of the intake port. Imperfect combustion of fuel results then.
Furthermore, with increasing demand for better characteristics, conventional carburetors developed to the present day have become complicated precision devices, which makes manufacturing thereof difficult and expensive. On the other hand, fuel injection systems, each requiring a fuel pump, a high-pressure pipe, a regulator, and a nozzle are complex and costly. Since operating pressure is high, sealing of pipes and of the pump requires special attention to prevent leakage. A collision or burst of the pipes will causes fuel spurt out, forming fuel vapor which is readily ignited by a spark or heat. This is a severe safety drawback.
For the reasons just given, conventional fuel supply systems have considerable shortcomings. This has brought up micro-pulsation pumps as means for supplying fuel. Therein, micropumps are placed at the intake pipe of an internal combustion engine, vaporizing and ejecting fuel into the inlet. Thus fuel which is completely mixed with air enters the cylinder. Being products of mature technology, micropumps are inexpensive. Furthermore, micropumps operate at low pressure, thus there is no need to add a pressurizing system. This keeps down costs, and there is no risk of explosion due to broken pipes. Moreover, micropumps are capable precisely to dose fuel, ejecting fuel droplets ejected at medium speed, so completely mix with air. Therefore, no wetting of walls of intake pip will occur, and combustion in the engine will be more effective.
As shown in FIG. 8, the micropump array 80 is manufactured using a micro-fabrication process, having a plurality of elements arranged in rows, with corresponding nozzles 81, 50 that tiny droplets are ejected. Thus the fluid is ejected as fine vapor and evenly distributed in the surrounding air. As shown in FIGS. 9 and 10, the micropump array 80 is a thermal tubble micropump or a piezoelectric micropump.
As shown in FIGS. 9-11, a thermal bubble micropump, which is conventional, has a substrate 90, enclosing one chamber 91 or a plurality of chambers 91, a heating plate 93 and a conduit (not shown), allowing the fluid to enter the chambers 91. Furthermore, a nozzle plate 92 is glued to the substrate 90, having one nozzle 81A or a plurality of nozzles 81A, with each nozzle 81A being connected with one of the chambers 91. When the fluid enters the chambers 91, intermittent heating of the heating plate 93 vaporizes the fluid, causing tiny droplets 95 thereof to be ejected through the nozzles 81A, so that vapor is spread in the surrounding air.
As shown in FIG. 10, a piezoelectric micropump has a substrate 100, enclosing a chamber 101 which is covered by a nozzle plate 102. The nozzle plate 102 has a nozzle 81A. A vibrating plate 103 is placed opposite to the nozzle plate 102, with a piezoelectric plate 104 being attached to the vibrating plate 103. Vibrations thereof causes tiny droplets 105 of the fluid in the chamber 101 to be ejected through the nozzle 81A.
However, since a micropump operates without valves, underpressure of incoming fuel needs to be maintained to prevent fuel from leaking from the micropump due to gravitation. Furthermore, being placed in the inlet of the engine, inlet pressure varies with operational states of the engine, with underpressure of incoming fuel varying along. This causes the quantity of fuel furthered by the micropump to vary, as well. It is therefore desirable for achieving well-defined operation of the micropump to keep the underpressure of incoming fuel stable against the pressure of air in the inlet.
The main object of the present invention is to provide a micro-pulsation fuel injection system with underpressure stabilizer which maintains a stable underpressure of an inlet of the micropump against the exterior thereof in an intake pipe of an internal combustion engine, so that fuel is precisely delivered for effective combustion thereof.
The present invention has a compression pump at a fuel supply pipe of the micropump, for keeping underpressure of the inlet of the micropump against the intake pipe stable. Incoming fuel passes through a fuel chamber, separated by a membrane from a pressure chamber, which in turn is connected to the intake pipe. The membrane deforms according to pressure in the intake pipe, changing volume of the fuel chamber and generating underpressure of fuel therein.
The present invention can be more fully understood by reference to the following description and accompanying drawings.